1. Field of the Invention
The present invention relates to a path search method in a CDMA receiver, and more particularly to a path detection method which can reduce calculation time by adjusting the frequency of searching among a plurality of regions in which a searching for a peak electrical power is performed.
2. Related Art
In mobile communications in the past, in a DS-CDMA (direct sequence code division multiple access) receiver performing multipath access using spread spectrum, a delay profile is measured by a multipath search section, a number of paths having large signal power being selected within the measurement range, these paths being assigned to individual fingers, and the selected paths being synthesized in what is known as a Rake synthesis receiver. Each finger performs inverse spread of one assigned path, and establishes symbol synchronization.
In mobile communications, because of the non-uniformity of the propagation paths for each received signal when there are multiple signals propagated. Multiple waveforms exist having differing propagation delay times. In DS-CDMA communication, by using broadband spread encoding to spectrally spread narrow-band data, is possible to separate and extract the multiple signals having differing propagation delays in the form of a delay profile.
Because the position of a mobile station with relation to a base station varies, there is a change in the surrounding radio propagation environment, as well as in the associated delay profile.
In DS-CDMA communication, it is known that by using synthesis (known as Rake synthesis), in which a plurality of multipath signals having differing propagation delays are grouped together, it is possible to achieve a diversity effect, thereby improving receivability.
Because, as noted above, the constant movement of a mobile station relative to a base station, however, there is an accompanying change in the delay profile, resulting in a change in the delay time of the path to be synthesized by Rake synthesis. In a mobile communications environment, therefore, it is important to immediately track a change in the delay profile and to perform Rake synthesis so as to obtain the maximum signal power. In order to track the changes in the delay profile, multipaths searching and tracking functions have been used in the past.
The convention art, however, is accompanied by the following problem.
Specifically, in general a huge amount of calculations must be performed in order to perform the processing to search for an effective path from all of the data, which is generally a large amount of delay profile data. For this reason, there is the problem of an increase in the amount time and current consumption required for such processing increases, and the problem of an increase in the size of the hardware used for an actual hardware implementation.